M4 'Hourglass' Frame

I have a little gap between major projects at work, and I am successfully procrastinating on all the things I need to do in my life, so I decided to take a swing at designing a frame for my upcoming M4. I’m honestly not a big fan of the default frame- it doesn’t seem that rigid overall and from the calibration video it seems somewhat cumbersome. As a goal for myself, I wanted to design something at least no less rigid and no more cumbersome.

I wanted an 8 ft x12 ft anchor spacing and something that could be used either horizontally in a table configuration- not necessarily on the floor- or vertically. Although I am fairly proficient with a good collection of hand and power tools, I wanted a design that could be accomplished by someone with no more than basic tools and skill. I also wanted it to be affordable- with the default frame’s budget as a target.

I did a design sprint with four iterations, each time restarting with a clean sheet design utilizing insights from the previous iteration. This was completed last night, and I hadn’t intended to actually build it at this point, but my plans for the day fell through so this afternoon I went ahead and made a first article.

The overall dimensions are 8ft x12 ft, with the narrower middle section being 4 ft 8 in wide. No part of the table is more than 28 inches from the edge- it would have been almost impossible to manage an eight-foot wide table height workspace.

The belts are going to pass over the side cutouts in operation, so nothing fixed can be placed there, but there should be no issue with moving in and out of this space. There’s even a portion of the ends that will never be crossed by the belts, so some small items such as e-stop switches can be placed there. Furthermore, the M4 sled can be placed on the end when loading or unloading a sheet.

The top is a continuous shear web, so it is extremely rigid across the plane. There is also a continuous perimeter frame underneath. This mutually reinforces the frame and the panel, and since the panel does not have to support itself, it can be thinner.

I’m planning on using the 3D printed Triangle Anchors- I had them made in carbon-fiber reinforced PETG, which I have used before with great success.

I used what I had on hand, but I’m comfortable with the material choices. The build used two sheets of 7/16" OSB, three 8 ft 2x4s, and seven 8 ft 2x3s, but the design could be used unchanged with any sheet goods or lumber. Costing it out, it can be cheaper or at parity with the default frame. Not a design requirement, but I like to minimize waste, so this is all the scrap-

The last feature is that the entire thing breaks down into three pieces- the 4ft 8in x 8ft center section and the two ends, each of which with their extension is 4 ft x 8 ft. This makes it easier to store, and if needed makes it transportable in a pickup bed.


It’s a fantastic design across the board (pun intended), but it’s this last bit that really stands out to me. That is such a cool and useful feature.

Also the material usage is splendid! Almost no waste at all :grinning: :+1: :+1:


Wow! I still haven’t built my frame as I wanted to integrate it into an “island” of sorts in the garage, but you make a great point about distance from the edge, I hadn’t thought of that.

I thing building the center part as a permanent table, and adding the ends when I do CNC cuts with the M4 would make a lot of sense.


If anyone is interested, here are my own shop drawings- I’ve added a few dimensions, everything needed I think. It doesn’t show the bolts that attach the extensions to the central table, or the additional blocking in the corners. I’ll try to get around to a more approachable set of plans.

M4 Hourglass Frame.pdf (68.2 KB)

And here is the spreadsheet I used for cutting the 2xs.

Hourglass Frame V4.xlsx (18.7 KB)


I was thinking along the same lines, but the folding sawhorses worked for the first pass. :smile:

My plan is to use steel arms out of each corner of the workbench to hold the ends of the belts when required which can be removed when not needed.


Hey, just last night I was using what remained of the plywood sheet I’d just cut over some sawhorses as an assembly table. It might be a little while before I actually get to building my table, as I have a ton of other projects in the garage before that.


Very cool design. I was thinking about incorporating my workshop table to do the cutting and your design gives me some great ideas. My workshop table is 8 feet by about 30 inches, so I might put some out riggers on the sides and then the end sections at the ends of the table. Or just do what you did and mount/fasten it on to the table when I am doing CNC cutting.


Really impressed with this design, well done.